Friend in military intelligence taken in in the past (5)
I believe the answer is:
amigo
'friend' is the definition.
('friend' in Spanish)
'military intelligence taken in in the past' is the wordplay.
'military intelligence' becomes 'MI' (as in MI5 and MI6).
'taken in' indicates putting letters inside.
'in the past' becomes 'ago' (three years ago means three years in the past).
'mi' going inside 'ago' is 'AMIGO'.
'in' acts as a link.
(Other definitions for amigo that I've seen before include "Friend from Spain?" , "A Mexican pal" , "buddy abroad?" , "Hispanic friend" , "Quixote's friend" .)